1. Field of the Invention
The invention relates to a reflection-free termination of a TEM waveguide, in which a TEM wave is conducted through an inner conductor and an outer conductor and is absorbed at one end of the TEM waveguide by an RF absorber for absorbing the field energy and by an ohmic line termination for absorbing the conductor-guided energy of the TEM wave.
2. Discussion of Background
A device for EMI testing electronic equipment is known from Swiss Patent Application CH-2026/86-9. Compared with other test equipment, it exhibits great advantages in EMI testing (EMI=electromagnetic interference) electronic equipment. In particular, it creates a defined field distribution over a wide frequency range and can also be used for wide-band emission measuring.
However, it has been found that unwanted local and frequency-dependent inhomogeneities occur in the wave field. This is associated with the fact that the line termination is not sufficiently free of reflections.
A line termination for TEM waveguides is known, for example, from Offenlegungsschrift (German Patent) DE-31 30 487 Al. In particular, the inner conductor is there provided with terminating resistors which are located on equipotential lines, that is to say across the direction of propagation of the wave field. Measurements with such arrangements have shown, however, that these are not suitable for frequencies above 100 MHz.
A prior art TEM waveguide is illustrated in FIG. 7. The TEM waveguide opens out in a pyramid shape from its tip 2 at which a coaxial feeding bush is provided (not shown) via which a pulse or sinusoidal generator 14 may be connected to the TEM waveguide by means of coaxial cable 3. The TEM waveguide exhibits a closed outer line 1 having a rectangular cross-section. A plate-shaped inner line 4 of triangular shape is asymmetrically disposed in the waveguide, that is, the spacing from the top of outer line 1 to inner line 4 is smaller than the spacing from the bottom of outer line 1 to inner line 4. The TEM waveguide is closed on one end by a plurality of mutually adjoining pyramid-shaped highfrequency peak absorbers 6 which form absorber wall 5. Disposed in absorber wall 5 are terminal resistors 8.1, 8.2 and 8.3 which are used to terminate inner line 4 at contour point 4.1, 4.2 and 4.3, respectively. The absorber wall 5 is curved in the shape of a spherical segment. The center of curvature is situated in the region of the tip 2 of the TEM waveguide.
Also shown in FIG. 7 are measuring instruments 11 connected via cable 12 to system 13. System 13 is placed in the waveguide for testing the effect of electromagnetic fields on this system. It is apparent to one of ordinary skill in the art that the TEM waveguide may be of varying sized commensurate with the volume needed to appropriately test inserted system 13.